Laboratory testing showed that a half-dose booster increased antibody levels 37-fold. A higher, full booster dose drove antibody levels even higher - more than 80 times that of someone vaccinated with two jabs.
“I think it will protect people through the coming holiday period and through these winter months, when we're going to see the most severe pressure of Omicron,” said Dr Paul Burton, Moderna's chief medical officer.
The data, which has not yet been peer-reviewed, tested blood samples from people who had received the vaccine against a pseudovirus engineered to resemble the Omicron variant.
Britain’s medicines regulator has authorised a half dose (50 micrograms) for the Moderna booster and a full dose (100 micrograms) for primary vaccinations.
Moderna president Stephen Hoge said the company currently does not plan to pursue approval for a 100 microgram booster dose.
It may not be necessary to push up antibody levels even higher than those generated by the lower dose for many people, he said. Governments could, however, choose a higher-dose version if they want to confer an enhanced level of protection.
"Could higher be better? Absolutely. But do we have data on that today to make a conclusive recommendation? No," said Dr Hoge.
Pfizer's testing likewise found its Covid vaccine triggered a similarly big jump in Omicron-fighting antibodies. It uses the same mRNA technology as the Moderna jab.
Taken together, along with other studies, evidence points to the need to get boosted against Omicron.
However, results are based on laboratory tests that do not capture the full range of the body’s immune response against the virus.
Antibody levels predict how well a vaccine may prevent infection with the coronavirus but they are just one layer of the immune system's defences.
Other research suggests the vaccine still should induce good protection against severe disease from Omicron if people do experience a breakthrough infection.
Both Moderna and Pfizer are developing vaccines to better match the Omicron variant in case they're needed.